1. Field of the Invention
This invention relates to a print apparatus and a print method for causing a print head to eject ink onto a print medium for producing a print, and more particularly to a print apparatus and a print method for controlling the print head temperature, which rises due to ink ejection.
2. Description of the Related Art
Types of print heads mounted in an inkjet print apparatus include one using thermal energy to eject ink. Such a type of print head typically comprises a highly concentrated arrangement of a plurality of fluid paths for delivering ink and a plurality of print elements each comprising an electrothermal transducing element (heater) for causing film-boiling of the ink in the fluid path.
However, the print head structured as described above accumulates more and more heat as ink ejections are increasingly repeated, and this heat accumulation may present a problem. Such a heat-accumulation problem tends to arise more markedly upon aiming at realizing the higher-speed and higher-density output.
For example, as heat accumulates in the print head, bubbles occur and grow in the ink. The growing bubbles obstruct ink ejection from the ejection port.
The temperature of the print head may sometimes reach one hundred and several tens of degrees Celsius. As a result, there may be the possibility that a plastic component forming part of the print head is thermally deformed, abrupt thermal expansion causes peeling of a bonding part, or the ink remaining near the heater is scorched.
In addition, the temperature rise may possibly give rise to a deterioration of the fluid contact properties between the ink and the components of the head. In this event, electrode wiring is corroded, which causes electric damage to the print head, or the ink erodes the bonding area between the nozzle and the substrate which causes reduced contact properties. An area where a nozzle is formed may be deformed. As a result, there are many cases where the head life is reduced.
For the purpose of avoiding the detrimental effects resulting from such a heat accumulation problem, there is known a method for controlling the print method by detecting the temperature of the print head during the print operation and then comparing the detected temperature with a predetermined threshold. For example, a method is known in which, based on a temperature detected at the present moment and the image data for the next main scan, the temperature of the print head after completing the next main scan is estimated, and then a waiting time is determined in accordance with the estimated temperature (see Japanese Patent Laid-Open No. 2001-113678, for example).
However, with this method, the throughput is significantly reduced as compared with the case of not providing the waiting time. If the threshold temperature at which the waiting time is activated is set high, this makes it possible to decrease the frequency of carrying out the setting of the waiting time so as to restrict a reduction in the throughput. However, this increases the risk of the print head suffering a head failure due to an excessive temperature rise.
In this connection, in many cases, the phenomenon of failure of the print head is caused by a complex combination of factors, such as the materials of the components of the print head, the ink formulation and the mechanical structure of the print head. In one case the print head breaks down when the head temperature reaches one hundred and several tens of degrees Celsius. In another case the print head breaks down when the head temperature reaches a level of a few tens of degrees Celsius. In yet another case the print head momentarily breaks down due to temperature-induced deformation or the like, but in another case the temperature-induced phenomenon, such as ink erosion or the like, moderately accelerates. Because of this, a threshold temperature when a waiting time is provided between main scans for preventing the excessive temperature rise is typically set in such a manner as to prevent one of the phenomena, which are caused by at various temperatures and lead to head failures, from being caused at the lowest temperature. In this case, a great effect is provided for controlling the temperature to prevent the occurrence of a head failure. In spite of this, even in a process for forming a low duty image, a waiting time may be generated just by a slight increase in head temperature, resulting in a significant reduction in throughput.
The present invention has been made in light of the foregoing, and an object of the present invention is to provide an inkjet print apparatus and an inkjet print method which are capable of restricting an excessive temperature rise in a print head and minimizing a reduction in throughput.